Author Topic: Cold Cylinder #2 (Read 4979 times)

youngerthanmybike · « **on:** February 15, 2011, 04:08:46 PM »

Okay, here's the scoop - '78 550k.

Cylinder No 2 is cold at idle, warm after a few miles on the road.

I've done some searching and have narrowed down my issue, but would like some further guidance.
I replaced the spark plugs(it was time anyway).
I checked the spark against the block- it looks good.
After putting the new plug in, it doesn't look like there is any discoloration on the new plug from being fired.
I adjusted the valves(it was due for a check anyway)
I pulled all four float bowls, and cleaned the sediment out of them.
I pulled all four main jets and cleaned them as well.
With the float bowl off of carb #2 and the gas on, the float valve seems to work correctly.

What's next and can I do it with the carbs still on the bike?

fire113 · « **Reply #1 on:** February 15, 2011, 04:18:18 PM »

Hi youngerthanmybike,

...did You checked if the is a spark at the spark plug on #2 ?

Good luck...Georg

Duke McDukiedook · « **Reply #2 on:** February 15, 2011, 04:25:11 PM »

No, you need to pull the carbs off and give them a thorough cleaning- carb cleaner in every orifice and compressed air after that. Then you will need to synchronize your carbs with a manometer or gauges for 4 cylinder engines.

fire113 · « **Reply #3 on:** February 15, 2011, 04:28:58 PM »

...I would check if there is a spark at the plug before I would take the carbs off!
May be it is only a broken spark plug lead!

Good luck...Georg

Johnie · « **Reply #4 on:** February 15, 2011, 04:31:46 PM »

Well, you said spark is good on #2. If you are saying there was sediment in the bowls then you are better off doing a cleaning. Sediment is probably in all 4 carbs...just worst in #2. I take it that spark plug #2 is not wet with gas when you take it out either. Then be sure you check the inside of the tank. That is the place the sediment is probably coming from. You may need to do a good tank cleaning too. Nothing worse than to do a good carb rebuild and then plug them up again from crap in the tank.

youngerthanmybike · « **Reply #5 on:** February 15, 2011, 04:50:21 PM »

Yes, there is spark at #2.
I removed the plug from the block, put it back into the wire and held it against the block to ground it while I cranked the starter. It looks good.

I basically have the carbs off the bike now, and I pulled the needle and looked in from the topside, it looks pretty clean.

OldSchool_IsCool · « **Reply #6 on:** February 15, 2011, 06:21:24 PM »

Won't fire at idle, but fires fine at speed. I'm guessing a clogged slow jet due to sediment in the bowl. You can pull the slow jets out with pliers, just be careful not to crush them.

Also check the in-tank filter. Bet you have a hole in it.

Lenny55 · « **Reply #7 on:** February 15, 2011, 07:05:38 PM »

Had my tank lined last year, best hundred dollars I've ever spent I think. The tank wasn't super bad, but it only takes the smallest speck to foul up a jet, and pulling and cleaning the carbs is only fun for so long........

youngerthanmybike · « **Reply #8 on:** February 15, 2011, 08:01:10 PM »

Quote from: OldSchool_IsCool on February 15, 2011, 06:21:24 PM

Won't fire at idle, but fires fine at speed. I'm guessing a clogged slow jet due to sediment in the bowl. You can pull the slow jets out with pliers, just be careful not to crush them.

Also check the in-tank filter. Bet you have a hole in it.

I wouldn't say it fires "fine" at speed. I can still touch the header without scalding my hand. It's hard to tell if it's burning anything or if it's just warm because everything else is so hot.

I'll have to look up the in-tank filter.... I didn't know there was one. I do have a small in-line filter south of the petcock.

Oh, and I did do a rough compression check, and there is 100+ psi of pressure in the cylinder, so I at least know there's no big hole in my piston either.

seanbarney41 · « **Reply #9 on:** February 15, 2011, 08:51:21 PM »

Quote from: OldSchool_IsCool on February 15, 2011, 06:21:24 PM

Won't fire at idle, but fires fine at speed. I'm guessing a clogged slow jet due to sediment in the bowl. You can pull the slow jets out with pliers, just be careful not to crush them.

Also check the in-tank filter. Bet you have a hole in it.

x2 on the slow jet...

youngerthanmybike · « **Reply #10 on:** February 15, 2011, 09:07:21 PM »

If I remember correctly, the slow jet is the smaller brass jet next to the main jet right? It's not the tube that comes up from the bottom of the float bowl....Thanks, I'll look into that.

Looks like I'm going to have to clean and line my tank as well. Bummer. That's $50 I didn't need to spend right now. I'm trying to sell the bike, but that's not going to happen if it's only running on 3 cylinders.....

Duke McDukiedook · « **Reply #11 on:** February 15, 2011, 09:27:12 PM »

Yeah, if your tank is not lined or thoroughly clean (NO RUST AT ALL) don't waste your time cleaning those carbs yet.

seanbarney41 · « **Reply #12 on:** February 15, 2011, 09:29:09 PM »

you are correct on the jet, look inside your tank with a light, if it's not dirty or rusty your gonna be ok without a liner. Have you checked the strainer in the petcock?

phil71 · « **Reply #13 on:** February 15, 2011, 11:12:59 PM »

if you can still touch it after a run, it just aint firing. normally, after 5 minutes off the slow jet it would keep half your skin.
Check compression, double check spark, and if you have both, yank that carb.. likely full of that rust/gas jelly that only neglect can generate.

dave500 · « **Reply #14 on:** February 15, 2011, 11:54:51 PM »

check that plug cap restistance.

Mark M · « **Reply #15 on:** February 16, 2011, 01:27:58 AM »

The logical first steps to diagnostics.

There are two major elements to a cylinder firing, fuel and spark.
If you think the spark is good then the next question is do you have fuel?
When you pull a plug to check it you should be looking for both the elements, if you have
just been trying to run it and fuel is getting through then the plug should still be wet.

If you have both a spark and fuel then you are either getting too much of one or not enough of the other.
That is when you need to start doing some more in depth checking of components.

dave500 · « **Reply #16 on:** February 16, 2011, 01:42:10 AM »

it might spark ok in open air but under compression it might not,id be checking the caps before you do the carbs,its quite a simple check,might save you some bother,check the compression on that cylinder aswell,might have a dodgy valve,with it running,pull that plug cap off the plug,how much worse does it run?

youngerthanmybike · « **Reply #17 on:** February 16, 2011, 08:47:39 AM »

I can't very well pull the plug cap off of just #2 and see how it runs, because that cuts out #3 as well.

Well, first things first. I finally stuck a flashlight inside my tank.

Very nasty.

So, looks like I'm going to take care of that rust issue first, rather than cleaning out my carbs only to fill them with crap again. I'm looking at either just doing the nuts and bolts and calling it good, or maybe Por-15. I'll do some searching on here before I make a final decision. I'll be back soon with more info on the cold cylinder though.

dave500 · « **Reply #18 on:** February 16, 2011, 11:44:42 AM »

you could put another plug into that cap as its running or hold the wire end against the head.

OldSchool_IsCool · « **Reply #19 on:** February 16, 2011, 03:21:02 PM »

Or swap the #2 plug with say #1. If the trouble follows the plug, then you have that answered.

Can do the same trick with the cap too, just do them one at a time.

youngerthanmybike · « **Reply #20 on:** February 16, 2011, 04:19:29 PM »

So I checked the resistance in the caps just now with my multi-meter.

It's supposed to be 5 ohms right?

Here's what I've got:

#1 - 4.90
#2 - 4.28
#3 - 4.72
#4 - 5.03

Seems like a significant drop for #2.... could easily be my problem. Should I just replace all four?

OldSchool_IsCool · « **Reply #21 on:** February 16, 2011, 04:35:21 PM »

Should be 5,000 ohms. Are you sure you were getting single-digit readings? Could the meter scale been set to K-ohms?

youngerthanmybike · « **Reply #22 on:** February 16, 2011, 04:39:51 PM »

Whoops, must have had it on the wrong setting.
Just double checked, and yes I had it on the K-ohms setting.

mlinder · « **Reply #23 on:** February 16, 2011, 04:40:41 PM »

Quote from: youngerthanmybike on February 16, 2011, 08:47:39 AM

I can't very well pull the plug cap off of just #2 and see how it runs, because that cuts out #3 as well.

wut?

youngerthanmybike · « **Reply #24 on:** February 17, 2011, 06:33:10 PM »

Well, I ordered new plug boots....
Does it sound like that's the culprit, or is that within the acceptable range?

I would just swap the boots around to check myself, but the tank is off for cleaning....

OldSchool_IsCool · « **Reply #25 on:** February 17, 2011, 08:53:12 PM »

I think they are within reason if not actually within spec. But new caps will be nice and shiny clean and are relatively cheap.

youngerthanmybike · « **Reply #26 on:** February 19, 2011, 06:37:43 PM »

Whelp, I had somebody come by to look at my bike yesterday so I had to get it running.

Put the carbs back on, rigged up a temp gas tank with a water bottle and some tubing...

And it fired right up on all four cylinders. Sounded nicer than I remember, must have been running on 3 for longer than I'd like to admit. Whoops.

I don't know what did it, must have been something stuck in the carb, because nothing else changed yet. Then, today my new plug boots arrived, so I put them on. They do look nice and shiny.

Thanks for your help guys, I appreciate it.

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Author Topic: Cold Cylinder #2 (Read 4979 times)